The invention relates to an apparatus for endoscopic photography, and more particularly, to such apparatus in which an automatic exposure mechanism disposed within a light source unit that is in turn connected to an endoscope is controlled in response to a signal from a photometric circuit disposed within a photographic camera which is mounted on the endoscope.
With a conventional apparatus for endoscopic photography, a light source which emits light for the purpose of taking a picture is activated in synchronism with the closure of X- or FP-contacts which represent electrical contacts disposed within a camera for the purpose of synchronization.
However, with an apparatus for endoscopic photography of the type utilizing a light source unit in which a switching operation is made in response to a shutter release operation of the camera between a diagnostic light source used for illumination purpose and another photographing light source used for taking a picture, the use of X-contacts presents a difficulty in that since they are closed simultaneously with the opening of the shutter, a film surface is exposed to diagnostic illumination light which continues to be emitted during the switching time, thereby preventing an accurate control of the exposure. In addition, since the photometry for the purpose of an automatic exposure control is initiated concurrently with the closure of X-contacts, it is difficult to derive a precise estimation of a contribution to the exposure which results from the diagnostic illuminating light during the switching time. Consequently, the amount of the diagnostic illuminating light which is maintained during the switching time associated with the light source causes an error in the exposure.
Where FP-contacts are used, it is necessary to effect a switching operation from a light source associated with the diagnostic illumination to another light source used for taking a picture in timed relationship with the closure of a synchro-contact, which is closed 11.+-.3 msec before the shutter begins to be opened. However, the required switching control is very difficult to achieve, and a wrong timing in the switching operation disadvantageously causes an error in the exposure.